The maximization of the ergodic capacity was studied for MIMO-NOMA system with a pair of users in [1]}. To accommodate as many pairs of users as possible, the concept of signal alignment was devised to cancel out inter-pair interference within MIMO-NOMA framework in [2]}, [3]}. By using the signal alignment, the signal receptions between different pairs of users can be handled independently. Hence, the investigations of MIMO-NOMA in [1]}, [3]}, [2]} were essentially specific to single/multiple pairs of NOMA users. To support more than two users in each NOMA group, multi-user MIMO-NOMA transmission strategies were developed in [7]}, [8]} by leveraging group interference cancellation in conjunction with minimum mean square error (MMSE) detector. To meet dynamic QoS requirements in IoT communications, novel precoding and detection strategies were proposed for MIMO-NOMA systems to differ users' effective channel gains in [9]}. A coordinated multipoint (CoMP)-enabled NOMA scheme was proposed to attain an improved spectral efficiency in [10]}, where distributed single-antenna base stations (BSs) collaborate together to form a virtual MIMO. Nonetheless, most of the existing works assumed frequent feedback of channel state information (CSI) at the transmitter. This assumption leads to high energy consumption, signaling and computational overhead, which is apparently impractical for bandwidth-limited, energy-constrained and latency-sensitive IoT networks [11]}, [12]}. In [13]}, [14]}, more effective CSI feedback was considered into NOMA-MIMO schemes. For further suppression of system overhead, the sender was assumed to have only statistical knowledge of CSI [15]}, [16]}, [17]}, [18]}, [19]}. To be specific, the rate and outage performance was analyzed for single-stream MIMO-NOMA systems in [15]}. In regard to the similar systems, a power allocation scheme was further proposed for maximizing the ergodic sum rate in [16]}. Furthermore, a linear MIMO-NOMA model with complex-valued power coefficients was derived by considering multi-stream transmissions in [17]}. Unlike [15]}, [16]}, [17]} that assume independent fading channels, the joint design of power allocation and receive beamforming was developed for single-stream MIMO-NOMA systems with receive correlation in [18]}. Whereas, the outage performance of multi-stream MIMO-NOMA systems was examined in [19]} by considering transmit correlation.
